1. Field of the Invention
The invention relates to a ply with strength carriers embedded in an unvulcanized rubber mixture for the belt bandage of vehicle pneumatic tires, whereby the strength carriers in the ply run essentially parallel to one another and are hybrid cords that are made of a first twisted yarn with a high modulus of elasticity and a second twisted yarn with a low modulus of elasticity which are final-twisted together. Furthermore, the invention relates to a vehicle pneumatic tire containing a belt bandage of such a ply.
2. Discussion of Background Information
With vehicle pneumatic tires, in particular in high-speed use, in order to prevent a lifting of the tire through the centrifugal forces that occur when driving, it is known to provide a belt bandage with a vehicle pneumatic tire that in general features an air-impermeable inner layer, a radial carcass containing strength carriers and extending from the zenith area of the tire over the side walls into the bead area and being anchored there by wrapping high-tensile-strength bead cores, a rubber tread rubber located radially outside and featuring profile grooves, and a belt between the rubber tread rubber and the carcass. The belt bandage can be embodied in one ply or multiple plies, covers at least the belt edges and contains parallel strength carriers running essentially in the circumferential direction in the form of cords that are embedded in rubber.
In tire manufacturing, the bandage is applied in the form of plies with strength carriers embedded in an unvulcanized rubber mixture, which plies are wound or reeled onto the belt. The strength carriers for such plies are embedded in rubber, in that a number of thread-shaped strength carriers (that are essentially parallel and as a rule are thermally pre-treated and/or pretreated with an impregnation in the manner known to one skilled in the art for better adhesion to the embedding rubber) run through a calender or an extruder in the longitudinal direction to be covered with a rubber mixture. In the shaping and vulcanization of the tire, the tire lifts/expands as a rule in the shoulder area by approx. 1 to 2% and in the center area by approx. 3 to 4% compared to the unvulcanized green tire, when the green tire is wound on a flat drum.
In EP-B 0 335 588 and EP-B 0 661 179 hybrid cords are suggested for the strength carrier cords of the belt bandage. These hybrid cords are twisted together from yarns with a high modulus of elasticity and with a lower modulus of elasticity. In a tensile stress/strain diagram with slight elongation, the cords first exhibit a slight rise of the curve; with higher elongation, the curve then rises markedly. In this last area, a slight further elongation, e.g., of 6 to 7%, is associated with high energy consumption. In tire manufacturing, the cords should permit a sufficient lifting in the shaping and in the vulcanization mold so that the tire can be formed precisely, and after completion of the tire, they ensure good high-speed serviceability under driving conditions.
EP-B 0 661 179 describes plies with strength carriers embedded in an unvulcanized rubber mixture for the belt bandage of vehicle pneumatic tires. The strength carriers run essentially parallel to one another in the ply and are hybrid cords that are made of a first twisted yarn with a high modulus of elasticity of at least 30000 N/mm2 and a second twisted yarn with a low modulus of elasticity of no more than 20000 N/mm2. These are final-twisted together. In the ply for the belt bandage, the cord count E in cords per 5 cm ply width, the force F1 with a 2% elongation of the hybrid cord (elongation range that is relevant for the lifting in the manufacture of the tire) and the force F2 with a 6% elongation of the hybrid cord (elongation range that is relevant for high-speed driving) satisfy the following relationships: F1×E<60 kgf (≈588.4 N), F2×E>150 kgf (≈1471 N). In addition to ease of fabrication and durability, the tires with such a ply as a bandage have a reduced weight. However, it has been proven that tires with such a belt bandage still have disadvantages in abrasion behavior.